A day after the CIC gave its ruling, Congress termed it as an "adventurist" approach that would harm democractic institutions.
Its view was echoed by CPI(M) and BJP's ally JD(U), which also rejected the order passed by the quasi-judicial body.
"It is not acceptable. We totally disagree with it. Such adventurist approach will create lot of harm and damage to democratic institutions," AICC General Secretary Janardan Dwivedi told reporters here.
"Getting political parties entangled in such unnecessary things will damage the demcratic process. We simply cannot accept it," he said.
The CPI(M), in a statement, said it "cannot accept" the CIC order that political parties are to be treated as "public authorities" and brought under the purview of the Right to Information Act.
"This decision is based on a fundamental misconception about the role of political parties in a parliamentary democracy," it said, adding "This will interfere with and hamper the functioning of a political party."
Expressing "astonishment and shock", JD(U) chief Sharad Yadav said the order was "no way justified" as "political parties are not shops".
Asserting that "we are totally against this move", he wanted the central government to scuttle the CIC move.
BJP, however, felt nothing wrong in the CIC order.
"BJP is not against anything that brings transparency and accountability which is equally applicable to all. We will follow the law," said BJP spokesman Capt Abhimanyu.